Sub-Pennsylvanian Subcrop Map of Mississippian Units in the Salina Basin

by Michael W. Lambert

KGS Open File Report 88-37

Mapped Area

The subcrop map of Mississippian units in central Kansas covers a 32-county area and contains over 1,680 well-control points. Previous Mississippian subcrop maps for Kansas were presented by Merriam (1963) and by Thompson and Goebel (1968). However, they did not distinguish each individual formation and did not have the benefit of the present amount of well control.

The present map includes northern Reno, Sedgwick, and Butler counties along its southern margin and extends as far north as eastern Phillips and western Nemaha counties along the Kansas-Nebraska state line. Well control on the subcrop map is shown by black dots, but control extends beyond the mapped area in Kansas and into Nebraska in order to eliminate edge effects. The map includes most of the Salina basin and parts of the Sedgwick, Forest City, and Cherokee basins. Faulting control was taken from K.D. Newell's pre-Mississippian subcrop map for the same area (Newell, 1987).

Stratigraphic Terminology

The areas of no Mississippian subcrop and of Chattanooga Shale subcrop were taken from K.D. Newell's map and adjusted to honor areas of greater well control on this map. The Chattanooga Shale is herein defined to consist of both the black shale and overlying red and green shale found at the base of the Mississippian carbonates.

The Compton Limestone is the lowermost Kinderhookian carbonate and has sometimes been called "Choteau." On the basin of geophysical and lithologic log information, it is usually a limestone., sometimes a dolomitic limestone, and is rarely a cherty limestone.

Overlying the Compton is the Sedalia Dolomite/Northview Shale. The Sedalia and Northview are facies of the same formation. The Sedalia is a dolomite or shaly dolomite, and the Northview is a dolomitic shale of shale.

The Reed Springs/Gilmore City is a combination of the two most widely used names for the formation immediately above the Sedalia/Northview. It is commonly called "Reed Springs" in southern Kansas and "Gilmore City" in the northern part of the state. It may be a limestone or cherty limestone, and is more rarely a dolomitic limestone.

In Kansas the name "Fern Glen" has sometimes been used to describe the formation immediately above the Reed Springs/Gilmore City (Zeller, 1968), but here it is called the Keokuk-Burlington Formation to conform with terminology from the Mississippian outcrop in southwest Missouri. The upper part of this formation is a limy dolomite or dolomite limestone (Keokuk?), and the ;lower part is a cherty dolomite. (Burlington?). On geophysical logs a denser and more resistive unit is present on top of less dense and less resistive unit.

Meramecian Series formations are present in the central parts of the basins in the mapped area. These include the Warsaw, Salem, St. Louis, and Ste. Genevieve limestones/ Maples and Waters (1987) point out the Ste. Genevieve was originally classified as Chesterian, and they believe that crinoid biostratigraphic considerations warrant returning the Ste. Genevieve to the Chesterian Series. Unlike the underlying Meramecian formations, the Ste. Genevieve in the mapped area is everywhere silty or sandy. Thus, lithostratigraphy would appear to support Maples and Waters.

The Warsaw Limestone is mostly dolomitic limestone or cherty limestone. It is easily distinguished from the underlying Keokuk-Burlington Formation by the presence of thin shale units within the Warsaw. The Salem Limestone can be a dolomitic limestone, a limy dolomite, a dolomite, or a cherty dolomite. The St. Louis Limestone varies in composition from limestone to dolomitic limestone. The Ste. Genevieve Limestone is usually a limestone, and rarely and cherty limestone.

The informally named "Cowley formation" is not present in the mapped area but was encountered by a stratigraphic cross section constructed along the Kansas Oklahoma state lime. The cherty interval appears to replace the Kinderhookian through Meramecian formations found to the north, and may be related to the position of the shelf edge at the time of deposition. In places it is possible to distinguish "Cowley A" (ls. > dolomite) from the underlying "Cowley B" (ls. > dolomite > shale).

Salina and Sedgwick Basins

The part of the subcrop map is basically a syncline with an axis extending northwest from Sedgwick to Jewell counties. The Chattanooga Shale is the oldest subcropping formation shown on the map, and the Salem Limestone is the youngest. This is also shown on the Mississippian subcrop maps of Merriam (1963) and Thompson and Goebel (1968). However, Merriam does not show the Chattanooga subcropping along the western margin of the Salina basin, while in the present subcrop map the Chattanooga is present in this area as far north as Observe County.

The Sedalia/Northview in the Salina and Sedgwick basins is mostly Northview Shale except for an area of Sedalia Dolomite in Geary County and one well with Sedalia Dolomite in Harvey County. Both the Sedalia/Northview and Reed Springs/Gilmore City in Cloud County. North and west of the pinch out, the Keokuk-Burlington directly overlies the Compton Limestone.

There is doming against the upthrown (eastern) side of the Voshell and Halstead-Graber anticlines in McPherson and Harvey counties. Northeast-southwest trending linear features are present on the subcrop pattern of this map, and may be related to lineaments in the Precambrian basement rocks (Berendsen, 1987). One prominent linear feature in Riley County can be seen on the present subcrop map as well as those of Merriam and Thompson and Goebel.

The Salem Limestone is shown as subcropping continuously from northern McPherson to Mitchell County, whereas Merriam and Thompson and Goebel show the Salem subcrop in Mitchell County as an isolated outlier. It should be noted that well control is sparse in this part of the mapped area, and that either interpretation could be correct. ANother difference is the presence of an east-west anticlinal structure in McPherson County that is not mapped by Merriam or Thompson and Goebel. The Salem Limestone is absent over this anticline.

Forest City and Cherokee Basins

The Chattanooga Shale is the oldest subcropping formation mapped in the Forest City and Cherokee basins and the Ste. Genevieve is the youngest. On the present map the Ste. Genevieve is shown subcropping in Chase and Wabaunsee counties, whereas Thompson and Goebel do not indicate its presence in the mapped area and Merriam shows it only in the extreme southeastern corner of Wabaunsee. The Sedalia/Northview subcrop extends north into Nemaha County before pinching out, and is mostly Sedalia Dolomite. Doming is present on the downthrown (eastern) side of the Humboldt Fault in Nemaha and Pottawatomie counties.